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Akshata Anil Mane. / International Journal Of Advances In Case Reports, 2016;3(6):245-248.
e - ISSN - 2349 - 8005
INTERNATIONAL JOURNAL OF ADVANCES IN
CASE REPORTS
Journal homepage: www.mcmed.us/journal/ijacr
A CASE REPORT ON VARIANT TERMINATION OF SCIATIC
NERVE
Akshata Anil Mane
Department of Anatomy, K.J. Somaiya Medical College, Somaiya Ayurvihar, Eastern Express Highway, Sion,
Mumbai-400 022, Maharashtra, India.
Corresponding Author:- Akshata Anil Mane
E-mail: [email protected]
Article Info
Received 15/01/2016
Revised 27/02/2016
Accepted 12/03/2016
Key words: Sciatic
Nerve, Trifurcation,
Tibial Nerve,
Common Peroneal,
Lateral Sural
Cutaneous Nerve,
Popliteal Fossa, Sural
Nerve.
ABSTRACT
The sciatic nerve is the thickest nerve in the body. It leaves the pelvis via the greater sciatic foramen
below piriformis and descends between the greater trochanter and ischial tuberosity, along the back of
the thigh, dividing into the tibial and common peroneal (fibular) nerves at a varying level proximal to
the knee. During routine dissection for the first MBBS students, I observed an unusual termination of
the sciatic nerve on the back of the left thigh in the middle of the popliteal fossa of a 70 years old,
donated embalmed male cadaver in the Department of Anatomy, K.J. Somaiya Medical college, Sion,
Mumbai, India. The sciatic nerve terminated in the middle of the popliteal fossa into the tibial nerve
(1), common peroneal (fibular) and the tibial nerve (2) [sural nerve]. The photographs of the three
branches of the sciatic nerve were taken for proper documentation and for ready reference.
Conclusion: The trifurcation of the sciatic nerve is very rare. The knowledge of low level of
termination of sciatic nerve is important for clinicians and surgeons. Clinically, the sural nerve is
widely used for both diagnostic (biopsy and nerve conduction velocity studies) and therapeutic
purposes (nerve grafting). Thus, a detailed knowledge of the anatomy of the sural nerve and its
contributing nerves are important in carrying out these and other procedures.
INTRODUCTION
The sciatic nerve is 2 cm wide at its origin and is
the thickest nerve in the body. It leaves the pelvis via the
greater sciatic foramen below piriformis and descends
between the greater trochanter and ischial tuberosity, along
the back of the thigh, dividing into the tibial and common
peroneal (fibular) nerves at a varying level proximal to the
knee. Superiorly it lies deep to the gluteus maximus,
resting first on the posterior ischial surface with the nerve
to the quadratus femoris lying between them. It then
crosses posterior to the obturator internus, the gemelli and
quadratus femoris, separated by the latter from obturator
externus and the hip joint. It is accompanied medially by
the posterior femoral cutaneous nerve and the inferior
gluteal artery. More distally it lies behind adductor
magnus and is crossed posteriorly by the long head of
biceps femoris. Articular branches arise proximally to
supply the hip joint through its posterior capsule, these are
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sometimes derived directly from the sacral plexus.
Muscular branches are distributed to biceps femoris,
semitendinosus, semimembranosus and the ischial part of
adductor magnus.
The point of division of the sciatic nerve into the
tibial and the common peroneal nerve is very variable. The
common site is at the junction of the middle and lower
thirds of the thigh, near the apex of the popliteal fossa.
The division may occur at any level above this, through
rarely below it. It is not uncommon for the major
components to leave the sacral plexus separately, in which
case the common peroneal component usually passes
through piriformis at the greater sciatic notch while the
tibial component passes below the muscle [1].
The sciatic nerve supplies the knee flexors and all
the muscles below the knee, so that a complete palsy of the
sciatic nerve results in a flail foot and severe difficulty in
Akshata Anil Mane. / International Journal Of Advances In Case Reports, 2016;3(6):245-248.
walking. This is rare and usually related to trauma. The
nerve is vulnerable in posterior dislocation of the hip. As it
leaves the pelvis it passes either behind piriformis or
sometimes through the muscle and at that point it may
become entrapped (the piriformis syndrome; this is a
common anatomical variant but an extremely rare
entrapment neuropathy). External compression over the
buttock (e.g. in patients who lie immobile on a hard surface
for a considerable length of time) can injure the nerve. The
most common cause of serious sciatic nerve injury (and
consequent major medicolegal claims) is iatrogenic. It may
be damaged in misplaced therapeutic injections into
gluteus maximus. The safe zone for deep intramuscular
injections here is the upper outer quadrant of the buttock.
Sciatic nerve palsy occurs after total hip replacement or
similar surgery in 1% of cases. This can be due to sharp
injury burning from bone cement, traction from
instruments, manipulation of the hip, inadvertent
lengthening of the femur, or haematoma surrounding the
nerve or within its soft tissue coverings. The patient has a
foot drop and a high stepping gait. The sciatic nerve
bifurcates into two major divisions (tibial and common
peroneal), most commonly at the lower part of the
posterior compartment of the thigh Several authors have
reported variations on its division into the tibial and
common peroneal nerve from the sacral plexus to the lower
part of the popliteal space These anatomical variations may
contribute to piriformis syndrome, sciatica, coccygodynia
and muscle atrophy. This should be taken into account by
clinicians who are planning interventions around the sciatic
nerve and its division in the lower extremity. Higher level
of the sciatic nerve division is a relatively frequent
phenomenon [2]. The sural nerve (short saphenous nerve),
is a sensory nerve formed by the union of the medial sural
cutaneous with the peroneal anastomotic branch of the
lateral sural cutaneous nerve, passes downward near the
lateral margin of the tendo calcaneus, lying close to the
small saphenous vein, to the interval between the lateral
malleolus and the calcaneus. It runs forward below the
lateral malleolus, and is continued as the lateral dorsal
cutaneous nerve along the lateral side of the foot and little
toe (via a dorsal digital nerve), communicating on the
dorsum of the foot with the intermediate dorsal cutaneous
nerve, a branch of the superficial peroneal. In the leg, its
branches communicate with those of the collateral
branches of the common tibial, and common fibular nerve
[1].
CASE REPORT
During routine dissection for the first MBBS
students, I observed an unusual termination of the sciatic
nerve on the back of the left thigh in the middle of the
popliteal fossa of a 70 years old, donated embalmed male
cadaver in the Department of Anatomy, K.J. Somaiya
Medical College, Sion, Mumbai, India. The sciatic nerve
terminated in the middle of the popliteal fossa by giving 3
branches. The three branches given were the tibial,
common peroneal and sural nerves (Fig 1). The common
peroneal nerve was reduced in size due to the sural nerve,
which was almost as thick as the common peroneal
nerve.The sural nerve continues down the leg on the
posterior-lateral side, then posterior to the lateral malleolus
where it runs deep to the fibularis tendon sheath and
reaches the lateral tuberosity of the fifth toe. The
photographs of the trifurcation of the sciatic nerve were
taken for proper documentation and for ready reference.
Figure 1 showing the photographic presentation of the sciatic nerve terminating in the middle of the popliteal fossa by
giving three branches. The three branches given were the tibial nerve-1, common peroneal and tibial nerve-2 [sural
nerve]. Common peroneal nerve reduced in size due to the sural nerve, which was almost as thick as the common
peroneal nerve.
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Akshata Anil Mane. / International Journal Of Advances In Case Reports, 2016;3(6):245-248.
DISCUSSION
During embryological development at the base of
the limb bud, the nerves contributing to the lower limb
forms two plexuses (lumbar and sacral). Later, as the
elements from each of these plexuses grow out into the
limb, they are subdivided into dorsal and ventral
components, for the dorsal and ventral musculatures. The
sciatic nerve is formed when the large dorsal component of
the sacral plexus (common fibular nerve) and the ventral
component (tibial nerve) moves downward close together
[3]. A number of variations in the course and distribution
of the sciatic nerve have been reported. Bifurcation into its
two major divisions (common peroneal and tibial) may
occur anywhere between the sacral plexus and the lower
part of the thigh. The two terminal branches of the sciatic
may arise directly from the sacral plexus [4].
Pokorný et al, Ugrenović et al, Saleh et al studied
the different level of division of the sciatic nerve [5,6,7].
When the sciatic nerve divides in the pelvis, the common
peroneal nerve usually pierces the piriformis muscle. The
common peroneal nerve passes either through the
piriformis or above the piriformis [8,9]. The entire sciatic
nerve may pass through the piriformis causing the sciatica
[5]. The tibial nerve passing deep and common peroneal
nerve passing superficial to the superior gemellus has been
found in literature [6]. The trifurcation of sciatic nerve into
tibial, common peroneal and lateral cutaneous nerve of calf
has been observed [10] but the trifurcation of sciatic nerve
into tibial, common peroneal and sural nerves is not
documented in literature. Normally the sural nerve is
formed by medial sural cutaneous nerve arising from the
tibial nerve and lateral sural cutaneous nerve from the
common peroneal nerve. The knowledge of these
variations is important because the sural nerve is the most
frequently used sensory nerve in nerve transplantation.
Reports on variations and surgical application of the
variations of sural and peroneal communicating nerve are
available in literature [11].
The present case of trifurcation of the sciatic
nerve is important to surgeons who do the popliteal block
for leg surgery, because high divisions of sciatic nerve may
lead to failure of popliteal block anesthesia [12]. The thick
sural nerve in this case is ideal for nerve grafts. Since the
division of sciatic nerve is very low, its branches may
interfere in knee surgery. The knowledge of the trifurcation
of the sciatic nerve, seen in the present case is extremely
important to the surgeons dealing with popliteal
aneurysms. Although entrapment of the sural nerve is a
rare condition, the resultant pain can be debilitating for
patients.
A thorough knowledge of the trajectory of the
nerve is essential for establishing a diagnosis, as well as for
treatment.
Clinical significance
The trifurcation of the sciatic nerve is important to
the surgeons who perform the popliteal block for leg
surgery, because high divisions of sciatic nerve may lead to
failure of popliteal block anesthesia [13]. The sural nerve
sub serves a purely sensory function, and therefore its
removal results in only a relatively trivial deficit. For this
reason, it is often used for nerve biopsy, as well as the
donor nerve when a nerve graft is performed. The sural
nerve is the most frequently used sensory nerve in nerve
transplantations. It is either transplanted alone or together
with the other elements of the neurovascular stalk within
the superficial sural flap [14]. Clinically, the sural nerve is
widely used for both diagnostic (biopsy and nerve
conduction velocity studies) and therapeutic purposes
(nerve grafting). Thus, a detailed knowledge of the
anatomy of the sural nerve and its contributing nerves are
important in carrying out these and other procedures [15].
CONCLUSION
The existence of such variations should be kept in
mind by the surgeons dealing with popliteal aneurysms, by
the orthopaedicians dealing with fracture of the femur, the
radiologists while doing radio-diagnostic procedures e.g.
CT scan, MRI of the thigh, by anesthetists performing pain
management and also by the physiotherapists.
ACKNOWLEDGEMENT
The author is thankful to Dean Dr. Geeta Niyogi
Madam for her support and also thankful to the Head of
Department Dr. Sawant and all the staff members of the
Department of Anatomy. The author also acknowledges
the immense help received from scholars whose articles are
included as references in this paper.
CONFLICT OF INTEREST:
The authors declare that they have no conflict of interest.
STATEMENT OF HUMAN AND ANIMAL RIGHTS
All procedures performed in human participants
were in accordance with the ethical standards of the
institutional research committee and with the 1964
Helsinki declaration and its later amendments or
comparable ethical standards. This article does not contain
any studies with animals performed by any of the authors.
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